In recent years, considerable research has been focused on the development of a high-energy density electric double layer capacitors (EDLC's), which currently has an energy density of less than 10% of that for Lithium-ion battery (LIB). Among all the energy storage systems that have been investigated and developed in the last few years, Lithium-ion Capacitors (LIC's) have emerged to be one of the most promising because LIC's achieve higher energy density than conventional EDLCs, and better power performance than LIBs as well as being capable of long cycle life. LIC's contain a “pre-lithiated” LIB anode electrode and an EDLC cathode electrode. Fuji Co. proposed using a separate lithium (Li) foil as the third electrode to pre-lithiate the anode electrodes and this LIC structure results an electrochemical energy storage device with three electrodes (cathode, anode, and the sacrificed lithium metal electrode). This three-electrode structure LIC's require the use of the mesh-type current collector for both cathode and anode in order to enable the transportation of the lithium ions into and between the cathode and anode, which makes the cell design complicated and expensive to manufacture.
Three methods of pre-doping lithium into negative electrodes have been developed in our previous patents as shown from FIG. 1 to FIG. 3: Stabilized Lithium Metal Powder (SLMP), Li Pieces and Li Strips. For the SLMP method, the advantages are the following: (1) the Li loading weight can be accurately controlled; (2) there is no damage to the electrodes; (3) it is suitable for mass production of electrodes. The disadvantages for said SLMP method include: (1) there is a high Li reaction speed which may get out of control; (2) there is numerous gas generation after the formation of the LIC cell; (3) there are safety issues for the mass production of the SLMP based LIC's. For the Li Pieces method, the advantages are the following: (1) the Li loading weight can be accurately controlled; (2) there is less gas generation after formation of LIC's; (3) it is safe to produce such Li Pieces based LIC's in a dry room. The disadvantages of such Li Pieces method are: (1) the Li Pieces may damage the electrodes after being pressed onto the surface of the electrodes; (2) it is not suitable for mass production. For the Li Strips method, the advantages are the following: (1) the Li loading weight can be accurately controlled; (2) there is less gas generation after formation of LIC's; (3) it is suitable for mass production for LIC's; and (4) it is safe to produce such Li Strips based LIC's in a dry room. The disadvantages of such Li Strips method are: (1) the Li Strips may damage the electrodes after being pressed onto the surface of the electrodes.
To solve all the above four methods issues, the present invention has been developed. In the present patent, the anode is pre-doped with enough lithium ions by ultra-thin lithium films having small holes loaded on the surface of the negative electrodes as shown in FIG. 4. The small holes in the ultra-thin Li films are very important for the electrolyte penetration into the negative electrodes during the LIC soaking process. Compared with the conventional three-electrode LIC by Fuji Co., a separate lithium electrode is not needed, thereby making the manufacturing process simpler. Compared with the three methods of SLMP, Li Pieces and Li Strips, the method of ultra-thin Li films having holes has the following advantages: (1) there is no damage from thin Li films to the electrodes; (2) it is suitable for LIC mass production; (3) the Li loading weight can be accurately controlled; (4) there is less gas generation after formation of LIC's; and (5) it is safe to mass produce such ultra-thin Li films having small holes based LIC's in a dry room. The only possible disadvantages for present invention are: (1) the ultra-thin Li films are difficult to produce, and (2) the price for such ultra-thin lithium film may be higher. Our future work will be focused on solving these two issues related to present invention.
In this respect, before explaining at least one embodiment of the invention in detail it is to be understood that the invention is not limited in its application to the details of construction and to the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. In addition, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be considered to be, or regarded as limiting.
Numerous innovations for the method of negative electrode pre-lithiation have been provided in the prior art in recent years that are described as follows. Even though these innovations may be suitable for the specific individual purposes to which they address, they differ from the present design as hereinafter contrasted. The following is a summary of those prior art patents most relevant to this application at hand, as well as a description outlining the difference between the features of the Method of Negative Electrode Pre-lithiation for Lithium-Ion Capacitors and the prior art.
US pending Patent Application Publication No. 2016/0141596A1 of Uhm et al. provides a method of pre-lithiating a negative electrode, a surface of the negative electrode being lithiated by submerging a roll that is formed by rolling together a negative electrode, and the copper foil, both sides of which are rolled with metallic lithium, in an electrolyte solution.
Wherein this pending patent application publication describes a method of pre-lithiating negative electrode, it does not include the use of thin Li films having holes to be used in the method of negative electrode pre-lithiation or the manufacture of lithium loaded negative electrodes for a lithium-ion capacitor by lamination with a carbon electrode material such as graphite, soft or hard carbon or the like.
US pending Patent Application Publication No. 2016/0181594A1 of Balogh et al. describes methods for pre-lithiating negative electrodes for lithium-ion electrochemical cells. The methods include disposing a lithium metal source comprising a layer of lithium metal adjacent to a surface of a pre-fabricated negative electrode. The lithium metal source and electrode are heated to a temperature of ≥about 100 □. To transfer a quantity of lithium to the pre-fabricated negative electrode. This lithiation process adds excess active lithium capacity that enables replacement of irreversibly lost lithium during cell formation and cell aging, thus leading to increased battery capacity and improved battery life. The methods maybe batch or continuous.
Wherein this pending patent application publication describes the process for lithiating negative electrodes for lithium ion electrochemical cells, it does not include the use of thin Li films having holes to be used in the method of negative electrode pre-lithiation or the manufacture of lithium loaded negative electrodes for a lithium-ion capacitor by lamination with a carbon electrode material such as graphite, soft or hard carbon or the like.
Therefore, none of these previous efforts provides the benefits attendant with the present inventive Method of Negative Electrode Pre-lithiation for Lithium-Ion Capacitors. The present design achieves its intended purposes, objects and advantages over the prior art through a new, useful and unobvious combination of method steps and component elements, as is described in greater detail below.
In this respect, before explaining at least one embodiment of the Method of Negative Electrode Pre-lithiation for Lithium-Ion Capacitors in detail it is to be understood that the method is not limited in its application to the details of construction and to the arrangement of the components set forth in the following description or illustrated in the drawings. The Method of Negative Electrode Pre-lithiation for Lithium-Ion Capacitors is capable of other embodiments and of being practiced and carried out in various ways. In addition, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.